Many types of linear motors are currently made for many different applications. There are two basic types of linear motors, circular and flat. Circular motors include, voice coil motors, voice coil actuators, and linear motors—sometimes called tubular motors, and are generally used for high force, small distance motors. Circular motors generally use a central member that would be an armature in a rotary motor and an outer member that surrounds the central member and would be a field in a rotary motor. The armature of the rotary motor is the thruster in a linear motor and the field of the rotary motor is the forcer. Flat linear motors are linear motors that are laid out flat, with coils and magnets alongside each other, with linear bearings that constrain the moving member and are generally used for intermediate distance movement. This flat type of linear motor can include electromagnets on both the moving and stationary side, as recited in published US Patent Application 2017/0047821 A1. Flat linear motors include linear induction motors, which are well known with the widest use in mass transit trains over long distances, sometimes with magnetic levitation. These have been known for quite a while as evidenced by U.S. Pat. No. 782,312 which was granted on Feb. 14, 1905 for a magnetic levitation application. Linear synchronous motors are also used for mass transit trains and may use electro magnets for both the fixed magnet and the moving magnet with both driven by multi-phase synchronized electronic drive systems.
Today's linear motors utilized for rapid movements from fractional distances to several inches, generally use one or more coils, one or more permanent magnets and a control system that delivers power to the coil(s) to control movement of the linear motor. Current efforts to improve the power and electrical efficiency of small distance, high speed, linear motors has involved the use of more and more powerful permanent magnets, typically using rare earths such as neodymium. These rare earth permanent magnets are quite strong but very expensive and if subjected to heat, see decreases in their strength proportional to the increased heat, as do all permanent magnets. The decrease in strength at elevated temperature hampers the use of linear motors in some applications, such as in internal combustion engines (ICEs). The decrease in magnetic strength with elevated temperature varies from magnet to magnet, additionally decreasing with increasing temperature at slightly varying rates from magnet to magnet, resulting in a change that cannot be compensated for by standard equations.
Due to the deficiencies of these prior attempts, there remains the need to provide an efficient linear motor that can operate at elevated temperatures. The improved linear motor presented here can serve in many applications while subject to elevated temperatures, including in actuation systems for the poppet valves of an ICE that reduce cost, weight and complexity, while providing for fully independent control of the valve actuation parameters.